Why has God predestinated believers to such a glorious position?
God predestinated believers to this glorious position by His grace, not by a long period of training. At salvation He immediately places them equal with Christ as joint heirs, adopting them as children by Jesus Christ to Himself, right with Christ in the body, in Christ, and in the heavenlies.
Les teaches that adoption in Greek and Roman society involved training a young son so that when he came of age he could come alongside his father and have full responsibility. But Les explains that believers do not have to go through a long period of training and preparation. The moment they are saved, God immediately positions them equal with Christ the Son as joint heirs. This is all by the grace of God, who predestinated them to the glorious position of being right with Christ in the body, in Christ, and in the elevated position in the heavenlies. They are predestinated unto the adoption of children by Jesus Christ to Himself.